This invention relates to a process for the passivation of crystal defects or grain boundaries or internal grain defects or surfaces in an electrically conductive material, and it relates, more particularly, to a process wherein the passivation is achieved by influencing suitable ions on the electrically conductive material.
In polycrystalline silicon, in contrast to monocrystalline silicon, due to the result of the occurrence of recombination effects at grain boundaries and internal grain defects, reductions in quality are likely in the solar cells produced from polycrystalline silicon. In recent years various processes have been proposed whereby such recombination effects is reduced or eliminated. Most of these processes are based on exposing the silicon wafers to an atmosphere containing hydrogen. In this hydrogen treatment of the silicon wafers, Si--H.sub.x -bonds can occur which passivate the "dangling bonds" at grain boundaries and at internal grain defects. The effective diffusion length of the charge carriers is thus increased and the life duration of the minority charge carriers is improved. This means that the light output of a solar cell produced from a silicon wafer of this type is increased.
Conventional hydrogen passivation processes are based on:
(a) hydrogen ion bombardment from a Kaufmann-ion source onto a cold or heated substrate, PA0 (b) the action of a high-frequency-hydrogen-gas discharge plasma on a cold or heated substrate, PA0 (c) the action of a DC-hydrogen-gas discharge-plasma on a cold or heated substrate, PA0 (d) treatment of a substrate in a molecular hydrogen atmosphere at temperatures of around 600.degree. C.